1. Field of the Invention
The present invention relates to a voltage control apparatus for an electric generator mounted on an automobile or motor vehicle (hereinafter referred to as the vehicle-onboard electric generator). More particularly, the present invention is concerned with a voltage control apparatus for a vehicle-onboard electric generator which apparatus can ensure easy availability of a starting or triggering signal regardless of occurrence of abnormality in a charge lamp.
2. Description of Related Art
For having better understanding of the concept underlying the present invention, description will first be made in some detail of a conventional voltage control apparatus for a vehicle-onboard electric generator. FIG. 7 is a block diagram showing generally and schematically an exemplary arrangement of a hitherto known or conventional voltage control circuit for a vehicle-onboard AC generator or alternator which is disclosed, for example, in Japanese Patent Publication No. 2707616.
Referring to FIG. 7, reference numeral 2 denotes a vehicle-onboard electric generator (alternator). For regulating or controlling the output voltage of the vehicle-onboard electric generator, there is provided a voltage control circuit (regulator) denoted generally by reference numeral 1. The voltage control circuit 1 is provided with an output terminal B which is electrically connected to the output terminals of the vehicle-onboard generator 2 and a battery 6, respectively, a lamp input terminal L, a monitoring output terminal FR connected to an external control unit 5 and a control input terminal G.
The voltage control circuit 1 is so designed that operation thereof is triggered or started when the voltage applied to the lamp input terminal L exceeds a predetermined value. Applied to the lamp input terminal L is a battery voltage VB supplied from the battery 6 by way of an ignition switch 3 and a charge lamp 4.
The vehicle-onboard electric generator 2 is comprised of a field coil 21 provided in a rotor (not shown) which is interlocked with an internal combustion engine (not shown), an armature coil 22 provided in a stator (not shown either) and a full-wave rectifier 23 for performing full-wave rectification of a three-phase generator voltage derived from the armature coil 22.
The full-wave rectifier 23 is implemented in the form of a three-phase parallel-connected diode bridge circuit. The field coil 21 and the full-wave rectifier 23 have respective ends both connected to the output terminal of the battery 6.
The external control unit 5 constituted by a conventional electronic control unit (hereinafter also referred to as the ECU in short) is designed not only to generate a starting or trigger signal for starting or triggering operation of the voltage control circuit 1 but also to acquire an abnormality message signal issued by the voltage control circuit 1 to thereby stop or interrupt the operation of the voltage control circuit 1.
To this end, the external control unit 5 is composed of a CPU (Central Processing Unit) 51 which is in charge of controlling the voltage control circuit 1 as well as operation of the engine, resistors 52, 54 and 55 connected to the CPU 51, a Zener diode 53 and an output transistor 56.
Connected to the external control unit 5 are a variety of sensors known in the art (not shown) for supplying to the external control unit 5 various detection signals such as an engine rotation number signal (engine speed signal) Ne indicating engine operation state inclusive of engine speed in rpm, a signal indicating a depression stroke of an accelerator pedal of the motor vehicle (hereinafter also referred to as the accelerator pedal depression stroke), a signal indicating cooling water temperature Tw and the like signal which are required for carrying out the operation control of the internal combustion engine.
On the other hand, the CPU 51 is provided with a power supply port a which is connected to a junction between the resistor 52 and the cathode of the Zener diode 53, and the battery voltage VB is applied to the power supply port a by way of the resistor 52. Further, the CPU 51 is provided with an operation triggering port b which is connected to the output terminal of the ignition switch 3 by way of the resistor 54. Furthermore, the CPU 51 is equipped with a monitoring input port c which is connected to the output terminal of the ignition switch 3 by way of the resistor 55 and additionally connected to the monitoring output terminal FR of the voltage control circuit 1.
In addition, the CPU 51 has a control output port d which is connected to the base of an emitter-grounded output transistor 56, the collector of which is connected to a control input terminal G of the voltage control circuit 1. In addition, the CPU 51 is equipped with a ground port e which is electrically connected to the ground potential.
The voltage control circuit 1 includes an output transistor 101 for controlling the electrical conduction ratio of the field coil 21 which corresponds to the field current of the electric generator 2 and a diode 102 electrically inserted between the collector of the output transistor 101 and the field coil 21. The output transistor 101 has a base electrically connected to the collector of a transistor 103 and additionally to a constant source voltage Vcc via a resistor 104. On the other hand, the base of the transistor 103 is connected to the output terminal of a comparator 105 which can be implemented by using a conventional differential amplifier.
The comparator 105 has a reference input terminal (-) which is connected to a junction of voltage dividing resistors 106 and 107 inserted in series to each other between the constant source voltage Vcc and the ground potential, while the comparison input terminal (+) of the comparator 105 is connected to a junction between voltage dividing resistors 108 and 109 which are inserted in series to each other between the output terminal of the vehicle-onboard generator 2 and the ground potential.
Further, the comparison input terminal (+) of the comparator 105 is connected to the collector of a transistor 112 by way of a resistor 110. On the other hand, the base of the transistor 112 is connected to the constant source voltage Vcc by way of a resistor 111.
Further, the voltage control circuit 1 includes a diode 113 connected to a one-phase output terminal of the armature coil 22, a capacitor 114 connected between the cathode of the diode 113 and the ground potential, a series connection of a diode 115 and a transistor 116 inserted between the lamp input terminal L and the ground potential, and a diode 117 inserted between the monitoring output terminal FR and the field coil 21.
In the voltage control circuit 1, the monitoring output terminal FR is connected via the diode 117 to the output transistor 101 which is designed to serve for voltage application control of the field coil 21.
Furthermore, the voltage control circuit 1 includes a fault diagnosis circuitry 118, a power generation detecting circuitry 119, an L-terminal level discriminating circuitry 120, an operation trigger circuitry 121 and a constant-voltage power supply circuitry 122.
The power generation detecting circuitry 119 is connected to the one-phase output terminal of the armature coil 22 via a diode 113 for detecting the electric power generation state on the basis of the one-phase output terminal, where the signal indicating the result of the detection is supplied to both the fault diagnosis circuitry 118 and the operation trigger circuitry 121.
The fault diagnosis circuitry 118 is designed to drive the transistor 116 in dependence on the output signal of the power generation detecting circuitry 119, which signal indicates the detected electric power generation state. The L-terminal level discriminating circuitry 120 and the operation trigger circuitry 121 are inserted between the lamp input terminal L and the constant-voltage power supply circuitry 122.
Next, description will be directed to operation of the conventional voltage control apparatus for the vehicle-onboard electric generator implemented in the structure described above by reference to FIG. 7.
Referring to FIG. 7, upon closing of the ignition switch 3, the battery voltage VB is applied to the lamp input terminal L of the voltage control circuit 1 via the charge lamp 4.
In response to the application of the battery voltage VB, both the L-terminal level discriminating circuitry 120 and the operation trigger circuitry 121 incorporated in the voltage control circuit 1 are brought into operation, whereby the constant source voltage Vcc is supplied to the constant-voltage power supply circuitry 122 to thereby trigger operation of the voltage control circuit 1.
Simultaneously, upon application of the constant source voltage Vcc, operation of the comparator 105 is triggered with a base current being fed to the output transistor 101 via the resistor 104. Thus, the output transistor 101 is switched to the conducting state, which results in that a field current flows through the field coil 21. In this manner, the vehicle-onboard generator 2 is put into the state capable of electric power generation.
At this time point, however, the output signal of the comparator 105 is still in the state "OFF". Thus, the transistor 103 remains in the off-state (i.e., electrically nonconducting state). Further, since the power generation signal (i.e., signal indicating the electric power generation) is not yet inputted to the electric power generation detecting circuitry 119 designed for detection of the one-phase output power of the vehicle-onboard generator 2, the transistor 116 is turned on (i.e., switched to the electrically conducting state) through the medium of the fault diagnosis circuitry 118, causing the charge lamp 4 to light.
Now, let's suppose that the vehicle-onboard electric generator 2 starts electric power generation upon starting of operation of the engine of a motor vehicle. Then, the power generation detecting circuitry 119 detects the voltage as generated. As a result of this, the transistor 116 is turned off through the medium of the fault diagnosis circuitry 118, which results in extinction (deenergization) of the charge lamp 4.
Subsequently, when the generated voltage supplied from the vehicle-onboard generator 2 rises, the voltage applied to the comparison input terminal (+) of the comparator 105 will increase. More specifically, a voltage resulting from voltage division of the generated voltage through cooperation of the voltage dividing resistors 108 and 109, the resistor 110 and the transistor 112 is applied to the comparison input terminal (+) of the comparator 105.
On the other hand, a reference voltage derived from the constant source voltage Vcc through voltage division by the voltage dividing resistors 106 and 107 is applied to the reference input terminal (-) of the comparator 105. Thus, when the voltage applied to the comparison input terminal (+) becomes higher than the reference voltage applied to the reference input terminal (-), the output signal of the comparator 105 assumes the state or level "ON".
Consequently, the transistor 103 is turned on while the output transistor 101 is turned off.
In this way, every time the divided voltage derived from the generated voltage exceeds the reference voltage, the output transistor 101 is turned off, whereby the field current is caused to decrease with the generated voltage being lower.
By contrast, the voltage resulting from the voltage division of the generated voltage becomes lower than the reference voltage inclusive, the transistor 103 is turned off, which results in that the output transistor 101 again assumes the conducting state (on-state), which leads to increasing of the field current and hence to rising of the generated voltage.
Through repetition of the operations described above, the conduction ratio of the field coil 21 is so regulated that the generated voltage of the vehicle-onboard generator 2 is controlled to remain substantially constant at a predetermined value.
Outputted from the monitoring output terminal FR of the voltage control circuit 1 is a monitor signal indicative of the conduction ratio of the field coil 21, which signal is fed to the monitoring input port c of the CPU incorporated in the external control unit 5. In this way, the CPU 51 is capable of monitoring changes of the conduction and nonconduction states (on- and off-states) of the output transistor 101 on the basis of the signal which indicates the state of the monitoring input port c and which is supplied to the CPU 51 via the resistor 55 to thereby determine discriminatively the electrical conduction ratio (which may also be termed the current conduction ratio) of the field coil 21.
Furthermore, when the transistor 56 incorporated in the external control unit 5 is turned on, a control signal is applied to the control input terminal G for changing over the generated voltage, the transistor 112 incorporated in the voltage control circuit 1 is turned off. In this way, the voltage control circuit 1 serves for changing the generated voltage of the vehicle-onboard electric generator 2.
The voltage control apparatus for the vehicle-onboard electric generator described above by reference to FIG. 7 however suffers a problem that upon occurrence of abnormality such as disconnection of wiring for the charge lamp 4, the voltage control circuit 1 of the vehicle-onboard generator 2 remains yet to be activated even when the ignition switch 3 is closed, incurring thus such undesirable situation that the vehicle-onboard generator 2 does not start the electric power generating operation even after the engine operation has been started.
Further, as can be seen from the figure, in the case where the control input terminal G for changing over the generated voltage and the monitoring output terminal FR for monitoring the electrical conduction ratio of the field coil 21 are required individually, the amount of wiring inclusive of connectors for both the control input terminal G and the monitoring output terminal FR increases, bringing about a problem in respect to the manufacturing cost of the voltage control apparatus as a whole. Namely, high cost will be involved in manufacturing the voltage control apparatus.
In recent years, there exists a trend of the lamps (or LEDs (Light Emission Diodes)) for charge indication, alternator fault alarm and others being driven by the external control unit 5, replacing the voltage control circuit 1 of the vehicle-onboard generator 2.
Consequently, the lamp input terminal L of the voltage control circuit 1 which is rendered unnecessary for the lamp driving naturally tends to be removed in view of reduction of the wiring cost. In that case, other type of trigger means will have to be provided.
As will be appreciated from the foregoing, in the conventional voltage control apparatus for the vehicle-onboard generator, the voltage control circuit 1 is put into operation in response to the trigger signal supplied by way of the charge lamp 4 and the lamp input terminal L. Accordingly, upon occurrence of abnormality in association with the charge lamp 4, operation of the voltage control circuit 1 remains yet to be triggered or started even when the ignition switch 3 is turned on (i.e., closed), thus making it impossible for the vehicle-onboard generator 2 to start the electric power generation to a serious problem.
Besides, it is noted that since the voltage control circuit 1 is provided with not only the lamp input terminal L but also the electric power generation output terminal B, the monitoring output terminal FR and the control input terminal G, respectively, lots of wirings are demanded, which aggravates complexity of circuit arrangement while providing a difficulty in realizing reduction of the manufacturing cost of the voltage control apparatus for the vehicle-onboard generator, giving rise to another problem.